Local energy absorber

ABSTRACT

A vehicle hood covering an underhood object includes an inner surface of the vehicle hood facing the underhood object and spaced from the underhood object, and an outer surface of the vehicle hood opposite the inner surface. A local energy absorber is operatively attached to the inner surface of the vehicle hood. The local energy absorber is a multiply-connected structure. The local energy absorber includes a wall defining an interior surface having symmetry about a central plane normal to the inner surface of the vehicle hood. A plurality of apertures is defined in the wall symmetrically about the central plane to initiate buckling and fracture in the wall during an impact applied to the outer surface defining an impact event having a duration of less than 20 milliseconds.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. application Ser. No.14/539,132, filed Nov. 12, 2014, which is incorporated by referenceherein in its entirety.

BACKGROUND

Some automobiles and other vehicles have a hood or bonnet, which is thehinged cover that allows access to the engine compartment formaintenance and repair. In many vehicles, but not all vehicles, the hoodor bonnet is on the front of the vehicle, relative to the forwarddirection of travel.

SUMMARY

A vehicle hood covering an underhood object includes an inner surface ofthe vehicle hood facing the underhood object and spaced from theunderhood object, and an outer surface of the vehicle hood opposite theinner surface. A local energy absorber is operatively attached to theinner surface of the vehicle hood. The local energy absorber is amultiply-connected structure. The local energy absorber includes a walldefining an interior surface having symmetry about a central planenormal to the inner surface of the vehicle hood. A plurality ofapertures is defined in the wall symmetrically about the central planeto initiate buckling and fracture in the wall during an impact appliedto the outer surface defining an impact event having a duration of lessthan 20 milliseconds.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a semi-schematic, perspective view of a vehicle having a localenergy absorber under a hood according to the present disclosure;

FIG. 2A is a semi-schematic, perspective view of the underside of thehood shown in FIG. 1, showing the local energy absorber of the presentdisclosure;

FIG. 2B is a semi-schematic, perspective exploded view of a hood with ahood inner panel, a hood outer panel, and a local energy absorberdisposed therebetween;

FIG. 3 is a semi-schematic, cross-sectional view taken substantiallyalong line 3-3 of FIG. 2A;

FIG. 4A is a semi-schematic, perspective view of the local energyabsorber depicted in FIG. 3;

FIG. 4B is a semi-schematic perspective view of examples of the localenergy absorber depicting stages of fabrication by extrusion accordingto the present disclosure;

FIG. 4C is a semi-schematic plan view of an example of a single sheet tobe folded into the local energy absorber depicted in FIG. 4D;

FIG. 4D is a semi-schematic, perspective view of an example of the localenergy absorber after the single sheet of FIG. 4C has been folded andpermanently joined at the free edges;

FIG. 5 is a semi-schematic side view depicting an example of an impactevent according to the present disclosure;

FIG. 6 is a semi-schematic, perspective view of local energy absorberhaving a wall defining a right circular cylinder according to thepresent disclosure;

FIG. 7A is a semi-schematic side view of a local energy absorber havinga wall defining a conical frustum according to the present disclosure;

FIG. 7B is a semi-schematic plan view of a single sheet to be rolled andpermanently joined to form the local energy absorber depicted in FIG.7A;

FIG. 8A is a semi-schematic perspective view of a local energy absorberhaving a wall defining a right stadium cylinder according to the presentdisclosure;

FIG. 8B is a semi-schematic top view of the local energy absorberdepicted in FIG. 8A;

FIG. 9A is a semi-schematic perspective view depicting an example of alocal energy absorber with a wall defining a right elliptical cylinderand a top flange;

FIG. 9B is a semi-schematic perspective view depicting the example ofFIG. 9A after an impact event similar to the impact event depicted inFIG. 5; and

FIG. 10 is a resultant deceleration vs. time chart comparingdeceleration traces associated with an impact involving a vehicle hoodwith and without a local energy absorber of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a semi-schematic, perspective view of an example of a vehicle10 according to the present disclosure. An underhood object 14 is shownin dashed lines. The underhood object 14 represents components withinthe engine compartment below the hood 12. FIG. 2A shows the underside ofthe hood 12, and FIG. 3 shows a cross-sectional view taken substantiallyalong line 3-3 of FIG. 2A. The vehicle hood 12 is generally illustrativeof the forward region or the hood region of the vehicle 10. The vehicle10 is shown for illustrative purposes and demonstrates only one possibleenvironment into which the components described herein may beincorporated. The underhood object 14 may be, for example and withoutlimitation, an engine, a battery, a supercharger, a sway bar, a fluidfill port cap, or combinations thereof. As used herein, the term “rigid”is not used in an ideal sense, but represents relatively hard objects,or relatively heavy objects, that may provide a reactive force to animpacting object.

While the present disclosure is described in detail with respect toautomotive applications, those skilled in the art will recognize thebroader applicability of the disclosure. Those having ordinary skill inthe art will recognize that terms such as “above,” “below,” “upward,”“downward,” etc., are used descriptively of the figures, and do notrepresent limitations on the scope of the present disclosure. Anynumerical designations, such as “first” or “second” used are notintended to be limiting, and any specific component may be referencedwith any number unless specifically stated herein.

The vehicle hood 12 includes a hood panel 16 having an inner surface 18facing the underhood object 14 and an outer surface 19 opposite theinner surface 18. A local energy absorber 20 is operatively attached tothe inner surface 18 of the hood panel 16 of the vehicle hood 12, suchas through a bond 22. In other examples, the local energy absorber 20may be attached by, rivets, snap fits, or fasteners (not shown). Thelocal energy absorber 20 is a multiply-connected structure, and isattached to the hood panel 16 adjacent to the underhood object 14.

The bond 22 may be, for example and without limitation, an adhesive bondor a welded bond. The local energy absorber 20 may be attached to theinner surface 18, or disposed between the inner surface 18 and theunderhood object 14 in the engine compartment of the vehicle 10. In somevehicles 10, the hood 12 may include a hood outer panel 17, and a hoodinner panel 11. The hood outer panel 17 may have the outer surface 19,which is the surface that is visible from outside the vehicle 10 (seeFIG. 1) when the hood 12 is in a closed position as shown in FIG. 1. Thehood inner panel 11 may have a supporting rib structure 13 as depictedin FIG. 2B. In the example depicted in FIG. 2B, the local energyabsorber 20 may be operatively attached to the inner surface 18 bypositioning the local energy absorber 20 between a hood inner panel 11and the hood outer panel 17. When disposed between the hood inner panel11 and the hood outer panel 17, the local energy absorber 20 may beplaced on edge supports (not shown) to receive the local energy absorber20 so that a portion of the absorber is unsupported except for contactaround the outer edges to prevent the local energy absorber 20 fromslipping away from the mounting location.

In some vehicles 10, the local energy absorber 20 may be attached to theinner surface 18 indirectly. For example, the hood inner panel 11 mayintervene between the local energy absorber 20 and the inner surface 18.In such an example, the local energy absorber 20 is attached to theinner surface 18 via the hood inner panel 11.

The multiply-connected structure or multiply-connected body of the localenergy absorber 20 is configured to absorb energy delivered by an impactload 24 to the outer surface 19 of the hood 12, such as from animpacting object 25. The impact load 24 is represented as an arrow, andis illustrative only. The direction and type of impact may vary and theimpacting object 25 causing the impact load 24 may vary.

The inner surface 18 of the hood panel 16 is spaced from the underhoodobject 14 by a basin depth 26. The basin depth 26 may be defined ormeasured in different ways. In FIG. 3, the basin depth 26 is shown asthe shortest absolute distance between the inner surface 18 and theunderhood object 14. However, an alternative measurement may be madealong a line substantially parallel to the expected direction of theimpact load 24, which is shown as alternative basin depth 27.

If the local energy absorber 20 were not attached to the hood panel 16,the impact load 24 may cause the hood panel 16 to deform until the hoodpanel 16 crosses the basin depth 26 and makes contact with the underhoodobject 14. However, the local energy absorber 20 is to deform anddissipate energy from the impact load 24 before the hood panel 16 (orthe hood inner panel 11) makes contact with the underhood object 14,thereby reducing the force applied by impact with the underhood object14. The way in which the local energy absorber dissipates the impactload 24 may be quantified using Eq. 1 below. Without the local energyabsorber 20, the peak loads experienced by the impacting object 25 arehigher and less energy is absorbed (by the hood 12) as the impactingobject 25 passes through the basin depth 26 with the hood 12 between theimpacting object 25 and the underhood object 14.

$\begin{matrix}\left\{ {\left( {t_{2} - t_{1}} \right)\left\lbrack {\frac{1}{t_{2} - t_{1}}{\int_{t_{1}}^{t_{2}}{{a(t)}\ {t}}}} \right\rbrack}^{2.5} \right\}_{\max} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

In Eq. 1, t₁ and t₂ are the initial and final times (in seconds) of atime interval during which Eq. 1 attains a maximum value, anddeceleration a is in units of gs (1 standard g=9.81 meters per secondsquared). The maximum time duration (t₂-t₁) may be limited to a specificvalue ranging from about 3 ms to about 36 ms (milliseconds). Forexample, the maximum time duration may be about 20 ms.

In experimental tests, Eq. 1 is evaluated from the deceleration and timehistory of at least one accelerometer mounted at the center of gravityof the impacting object 25 when the impacting object 25 is impacted intothe hood panel 16. Eq. 1 evaluates the effects of the deceleration onthe impacting object 25 and the duration time of the deceleration. Insome computer models that predict a value of Eq. 1 for an impactscenario, higher scores result from either: short impact duration timesat larger maximum decelerations, or longer impact duration times atsmaller maximum decelerations. For a given basin depth 26, the localenergy absorber 20 of the present disclosure is to minimize or reducethe value of Eq. 1 for a particular impact scenario. Alternatively, thelocal energy absorber 20 may achieve a target value of Eq. 1 for aparticular impact scenario while minimizing the basin depth 26.

Referring to FIG. 4A, the local energy absorber 20 is amultiply-connected structure, including a wall 40 defining an interiorsurface 42 having symmetry about a central plane 46 normal to the innersurface 18 of the vehicle hood 14. A plurality of apertures 50 isdefined in the wall 40 symmetrically about the central plane 46 toinitiate buckling and fracture in the wall 40 during an impact appliedto the outer surface 19. In examples, the impact defines an impact eventhaving a duration of less than 20 ms. In other examples, the impactevent may have a longer or shorter duration.

As used herein, the term “singly-connected structure” refers tostructures or bodies in which any mathematical circuit 38 drawn within across section of the body can be reduced to a single mathematical point.The mathematical circuit 38 is a closed, continuous curve, and amathematical point has no dimension and can be referenced only by itslocation. As the mathematical circuit 38 is reduced to smaller andsmaller circuits, it will eventually converge to a point. In the presentcontext, singly-connected bodies or structures may also be referred toas open-shell structures. In a singly-connected structure, every closedcurve or mathematical circuit 38 within the cross-section can be cappedwith a closed surface, i.e., a surface without any holes.

In sharp contrast, a single mathematical circuit within“multiply-connected structures” cannot be reduced to a single point.Similarly, mathematical circuits of multiply-connected structures cannotbe capped by closed surfaces. As a general rule, multiply-connectedstructures have holes in them, while singly-connected structures do not.

As used herein, a structure may be singly-connected in firstcross-sections transverse to a first direction 48, andmultiply-connected in second cross-sections transverse to a seconddirection 49 orthogonal to the first direction 48. FIG. 4A depicts amathematical circuit 38′ in an example of the second cross-sectiontransverse to the second direction 49. The mathematical circuit 38′ isprevented from being reduced to a point by the opening defined byinterior surface 42. In examples of the present disclosure, the firstdirection may be normal to the inner surface 18 of the vehicle hood 12,and the first direction may lie in the central plane 46. The seconddirection 49 may be orthogonal to the first direction 48 and the seconddirection 49 may also lie in the central plane 46. In examples of thepresent disclosure, the local energy absorber 20 is multiply-connectedin the first cross-sections transverse to the first direction 48 normalto the inner surface 18.

Illustrative examples of basic, cross-sectional shapes that are singlyconnected include, without limitation: C-shapes, S-shapes, or U-shapes.Illustrative examples of cross-sectional shapes that are multiplyconnected include, without limitation: ovals, boxes, and figure eights.The mathematical topology of multiply-connected structures renders theirstructural response during impact completely different from thestructural response of singly-connected bodies. In examples of thepresent disclosure, the multiply-connected structure is advantageous inthat it directly affects energy absorption on the local energy absorber20 causing Eq. 1 to yield a lower result.

In the example depicted in FIGS. 1-4A, the wall 40 includes a planar topportion 32 normal to the central plane 46. A planar bottom portion 34 isparallel to the top portion 32 and spaced from the top portion 32. Aplanar first side portion 36 is defined between the top portion 32 andthe bottom portion 34. A planar second side portion 37 is parallel tothe first side portion 36. The planar top portion 32 is operativelyattached to the inner surface 18 of the vehicle hood 12. The apertures50 are defined in the first side portion 36 and the second side portion37. The apertures 50 may define a header 96 (e.g. see FIG. 3) on thefirst side portion 36 and the second side portion 37 such that header 96prevents the apertures 50 from being defined in the intersection of theplanar top portion 32 and the first side portion 36 or the second sideportion 37. In the examples depicted in FIGS. 4A-4D, there is no header96, and the apertures 50 are defined through the intersection of theplanar top portion 32 and the first side portion 36. Similarly, theapertures 50 are defined through the intersection of the planar topportion 32 and the second side portion 37 in FIGS. 4A-4D.

Similarly, the apertures 50 may define a footer 98 on the first sideportion 36 and the second side portion 37 such that footer 98 preventsthe aperture 50 from being defined in the intersection of the planarbottom portion 34 and the first side portion 36 or the second sideportion 37. In the examples depicted in FIGS. 4A-4D, there is no footer98, and the apertures 50 are defined through the intersection of theplanar bottom portion 34 and the first side portion 36. Similarly, theapertures 50 are defined through the intersection of the planar bottomportion 34 and the second side portion 37 in FIGS. 4A-4D.

In examples of the present disclosure depicted in FIG. 4B, the localenergy absorber 20 may be fabricated by extruding the wall 40 as asingle extrudate 45 through a die 44, then forming the plurality ofapertures 50. In an example, the local energy absorber 20 may be formedfrom a magnesium alloy or an aluminum alloy. The plurality of apertures50 may be formed by machining, laser cutting, or other metal removalprocesses as the extrudate 45 exits the die 44 before the local energyabsorber 20 is divided from the extrudate 45. In the example depicted inFIG. 4B, a first laser 51 cuts the plurality of apertures 50 into theextrudate 45. A second laser 52 divides the local energy absorber 20from the extrudate 45. In other examples, another cutting device such asa rotary cutting tool (not shown) may be substituted for the first laser51 or the second laser 52.

The local energy absorber 20 is shown and described herein on thevehicle hood 12. However, the local energy absorber 20 may also be usedto reduce the effects of impacts to objects impacting other exteriorpanels or portions of the vehicle 10. For example, and withoutlimitation, the local energy absorber 20 may be located adjacent to:fenders, bumpers, or quarter panels. Note also that small holes (notshown) placed in the local energy absorber 20, such as holes in theplanar top portion 32 for attachment to the hood panel 16, do notcontribute to or detract from the multiply-connected nature of the localenergy absorber 20 because the response to impact loading would besubstantially unaffected by the small holes.

In the vehicle hood 12 shown in FIGS. 1-3, the planar top portion 32 andthe planar bottom portion 34 of the local energy absorber 20 aresubstantially parallel with each other and the inner surface 18 of thehood panel 16. As used herein, substantially parallel refers to theplanar top portion 32 and the planar bottom portion 34 being withinfifteen degrees of parallel, plus or minus. However, some examples maybe configured with the planar top portion 32 and the planar bottomportion 34 even closer to parallel, such as within five or fewer degreesof parallel.

Under sufficient impact load 24, the hood panel 16 deforms, and thelocal energy absorber 20 moves from the position shown in FIG. 3 towardthe underhood object 14 as depicted in FIG. 5. After the planar bottomportion 34 impacts the underhood object 14, the local energy absorber 20begins deforming and absorbs some of the energy of the impact load 24.

The multiply-connected structure of the local energy absorber 20 has adifferent deformation response than a singly-connected structure.Deformation without fracture occurs while the strain and displacement ofthe structures remain compatible. Structures maintain compatibility ofstrain and displacement for non-fracture deformation. The conditions fora compatible response to loading are dramatically different formultiply-connected structures and singly-connected structures.Therefore, singly-connected structures and multiply-connected structuresrespond to loading differently.

Some existing structures are configured to avoid fracture duringdeformation; however, the multiply-connected structure of the localenergy absorber 20 may be configured to fracture (after plasticdeformation and buckling) in response to the impact load 24 being abovea threshold load. Fractures are violations of compatibility between thestrain and displacement within the local energy absorber 20.Compatibility between strain and displacement refers to a continuumdescription of a solid body in which the solid body is described asbeing composed of a set of infinitesimal volumes. Each volume is assumedto be connected to its neighbors without any gaps or overlaps. Certainconditions have to be satisfied to ensure that gaps or overlaps do notdevelop when a continuum body is deformed. A body that deforms withoutdeveloping any gaps (e.g., cracks) or overlaps is called a compatiblebody. Compatibility conditions are mathematical conditions thatdetermine whether a particular deformation will leave a body in acompatible state. Before a crack develops, there is a relationshipbetween strain and displacement of the solid body. There iscompatibility between strain and displacement. After a crack develops,the previous relationship between strain and displacement is broken,violating the compatibility.

Prior to fracturing, the local energy absorber 20 may absorb energy.Upon fracturing, the local energy absorber dissipates energy from theimpact load 24 by opening up new surfaces in a subset 83 of theplurality of struts 81. The accumulation of excess strain energy withinthe absorber causes a crack to open some time after initial impact,which then dissipates strain energy into fracture propagation. Theenergy dissipated during fracture further prevents or minimizeshigh-energy contact between the underhood object 14 and the impactingobject 25. The fractures 88 may occur along a strut 89 (see FIG. 5) suchthat much of the energy dissipated by the local energy absorber 20 isdissipated by the strut 89.

In the local energy absorber 20 shown in FIGS. 1-3, themultiply-connected structure is shown as a metallic material, such asaluminum, magnesium, or alloys thereof. However, the local energyabsorber 20 may be formed from other materials, as described herein. Forexample, the local energy absorber 20 may be formed from ahigh-temperature polymer. As used herein, a high temperature polymermaintains its properties at temperatures above 150° C. up to 200° C.Examples of high-temperature polymers are polyamides (e.g. Nylon®),polyphenylene sulfide (PPS) and polyethersulfone (PES). The local energyabsorber 20 may include a filler material in a high-temperature polymermatrix. The filler material may be fiber, mineral or combinationsthereof. For example, the filler material may be carbon fiber, glassfiber, talc, or wollastonite, alone or combined. In examples, fibers mayhave an aspect ratio of around 20, and a length of about 200 μm to about300 μm. In other examples, fibers may range in length from about 2 mm toabout 5 mm. In still other examples, fibers may range in length fromabout 10 mm to about 25 mm.

The filler material may increase the strength/ductility of examples ofthe local energy absorber 20 made from a high-temperature polymer. Thefiller may decrease the ductility of the high-temperature polymer whenthe filler is added to the high-temperature polymer matrix. The fillermay be added to improve stiffness and strength of the local energyabsorber 20. The filler may inhibit crack growth by diverting crack tipsand/or blunting crack tips; thereby increasing the energy needed to formnew surface area. Ductility of the local energy absorber 20 may beincreased by adding the filler. Due to stiffening caused by the filler,it may take more force to reach the strain necessary to startpropagating cracks. However, the strain to fracture may decrease due tothe strain enhancement caused by the limiting amount of material thatcan be involved in dispersing the force.

In some configurations of the local energy absorber 20, the plurality ofstruts 81 moves from elastic deformation into fracture deformationsubstantially without plastic deformation. This may reduce Eq. 1resulting from the impact load 24 delivered by the impacting object 25.If the local energy absorber 20 is formed from magnesium or magnesiumalloys, the planar first side 36 and the planar second side 37 may movemore-directly between elastic and fracture deformation than if the localenergy absorber 20 is formed from aluminum. Magnesium alloys mayexperience very little plastic deformation between elastic deformationand fracture, but usually will experience some plastic deformation.

In examples of the present disclosure as depicted in FIG. 4C and FIG.4D, the local energy absorber 20 may be formed by folding a single sheet65 to form a closed perimeter 53, then permanently joining a first edge66 of the single sheet 65 to a second edge 67 of the single sheet 65 toform a seam 71 by crimping or welding. FIG. 4C depicts the single sheet65 as flat before being folded as indicated in FIG. 4D. The single sheet65 is folded at 90 degrees along the first folding line 92, the secondfolding line 93, the third folding line 94, and the fourth folding line95. It is to be understood that the corners at each of the folding lines92, 93, 94, and 95 are not necessarily sharp. FIG. 4D has planar firstside portion 36 and planar second side portion 37 depicted in hiddenline to indicate that the single sheet 65 is folded (as indicated byarrows 39 to form the closed perimeter 53. As used herein, permanentlyjoining means joining such that the single sheet 65 would be damaged byseparating the joint through application of a force to break the joint,or through a cutting process. For example, a crimped joint may form acold weld that cannot be separated without the weld pulling parentmaterial from one of the joined elements. The plurality of apertures 50may be formed in the single sheet 65 prior to the folding. In anexample, the plurality of apertures 50 may be stamped into the singlesheet prior to the folding.

FIGS. 6, 7 and 8A depict examples of the present disclosure having afirst intersection 54 of the wall 40 and a top plane 41 normal to thecentral plane 43. The first intersection 54 defines a first simpleclosed convex curve 56. A second intersection 58 of the wall 40 and abottom plane 55 parallel to the top plane 41 defines a second simpleclosed convex curve 57.

As used herein, a simple curve is a curve that does not cross itself;starting and stopping points may be the same. A closed curve is a curvethat starts and stops at the same point. A convex curve is a simple,closed curve with no indentations; the segment connecting any two pointsin the interior of the curve is wholly contained in the interior of thecurve.

In the examples depicted in FIGS. 4, 6, 8A, and 8B the second simpleconvex curve 57 is congruent to the first simple closed convex curve 56.In the example depicted in FIG. 6, the first simple closed convex curve56 is a circle 59, and the wall 40 defines a right circular cylinder 61.In examples depicted in FIG. 6, the diameter 74 of the circle 59 mayrange from about 25 mm to about 40 mm. The height 97 of the headers 96and the height 99 of the footers 98 may range from about 2 to about 10mm. The height 15 of the wall 40 may range from about 15 to about 40 mm.The thickness 23 of the wall 40 may range from about 1 mm to about 3 mm.The height 47 of the apertures 50 may range from about 10 mm to about 25mm. The width 90 of the apertures 50 may range from about 1.5 mm toabout 10 mm. The width 9 of the struts 89 may range from about 2.5 mm toabout 7 mm.

In the example depicted in FIGS. 8A and 8B, the first simple closedconvex curve 56 is a stadium 29, and the wall 40 defines a right stadiumcylinder 30. As used herein, a stadium means a geometrical oblong figureformed by joining semicircles to opposite ends of a rectangle. A rightstadium cylinder is a projection of a stadium normal to the plane of thestadium. In examples depicted in FIGS. 8A and 8B, the radius 21 of thesemi-circular ends 31 of the stadium 29 may range from about 10 mm toabout 30 mm. The length 28 of the parallel sides 33 may range from about40 to about 75 mm. The height 97 of the headers 96 and the height 99 ofthe footers 98 may range from about 2 to about 10 mm. The height 15 ofthe wall 40 may range from about 15 to about 40 mm. The thickness 23 ofthe wall 40 may range from about 1 mm to about 3 mm. The height 47 ofthe apertures 50 may range from about 10 mm to about 25 mm. The width 90of the apertures 50 may range from about 5 mm to about 15 mm. The width9 of the struts 89 may range from about 2.5 mm to about 7 mm. It is tobe understood that the ranges provided herein are non-limitativeexamples, and therefor examples beyond the expressly disclosed rangesare also disclosed herein.

In the examples having second simple convex curve 57 congruent to thefirst simple closed convex curve 56, (e.g. as depicted in FIG. 4A, FIG.6, and FIG. 8A) the local energy absorber 20 may be fabricated byextruding the wall 40 as a single extrudate through a die 44, thenforming the plurality of apertures 50 in the wall 40. In an example, thelocal energy absorber 20 may be formed from a magnesium alloy or analuminum alloy. The plurality of apertures 50 may be formed bymachining, laser cutting, or other metal removal processes as theextrudate 45 exits the die 44 before the local energy absorber 20 isdivided from the extrudate 45. In the example depicted in FIG. 4B, afirst laser 51 cuts the plurality of apertures 50 into the extrudate 45.A second laser 52 divides the local energy absorber 20 from theextrudate 45.

In the examples depicted in FIG. 6, an annular flange 72 is depicted inhidden line to indicate that some examples may exclude the annularflange 72, and some examples may include the annular flange 72. Theannular flange 72 is defined at the second intersection 58. In theexamples including the annular flange 72, the annular flange 72 may havean inner diameter 53 smaller than a diameter 54 of an inner circle 60defined at the second intersection 58.

In the examples depicted in FIG. 6, a top plate 77 is depicted in hiddenline to indicate that some examples may exclude the top plate 77, andsome examples may include the top plate 77. The top plate 77 is parallelto the top plane 41 and continuously connected to the wall 40 at thefirst intersection 54. For example, the top plate 77 may be continuouslywelded or bonded to the wall 40 at the first intersection 54.

In the example depicted in FIG. 7A, the wall 40 defines a conicalfrustum 64. The local energy absorber 20 may be fabricated from a singlesheet 65 (see FIG. 7B) by rolling the sheet to form the conical frustum64 then permanently joining a first edge 66 of the single sheet 65 to asecond edge 67 of the single sheet 65 to form a seam 71 by crimping orwelding. As stated above, permanently joining means joining such thatthe single sheet 65 would be damaged by separating the joint. Forexample, a crimped joint may form a cold weld that cannot be separatedwithout the weld pulling parent material from one of the joinedelements. In the example depicted in FIG. 7A, the plurality of apertures50 may be formed in the single sheet 65 prior to the rolling. In anexample, the plurality of apertures 50 defining the struts 89 may bestamped into the single sheet 65 prior to the rolling. In anotherexample, the plurality of apertures 50 may be formed in the conicalfrustum 64 by machining or laser cutting after the joining.

In the example depicted in FIGS. 8A and 8B, the wall 40 defines a rightstadium cylinder 30. An inner flange 75 is depicted in hidden line toindicate that some examples may exclude the inner flange 75, and someexamples may include the inner flange 75. The inner flange 75 is definedat the second intersection 58. The inner flange 75 has an inner edge 76defined parallel to the second intersection 58.

FIG. 9A depicts an example of a local energy absorber 20 with the walldefining a right elliptical cylinder 63. A top flange 77′ is parallel tothe top plane 41 and continuously connected to the wall 40 at the firstintersection 54. For example, the top flange 77′ may be continuouslywelded to the wall 40 at the first intersection 54.

FIG. 9B depicts the example of FIG. 9A after the impact event similar tothe impact event depicted in FIG. 5. The impact in FIG. 9B was centeredon the local energy absorber 20. Because of the centrality of loading ofthe impact, the progressive deformation from the major vertices 78 tothe center 79 is similar to the progression of deformation of thecentral struts 80 over time. The plurality of apertures 50 is defined bya plurality of struts 81 and a subset 83 of the plurality of struts 81is to, during the impact event, deform in a sequence beginning withelastic deformation, followed by plastic deformation and buckling,followed by fracture of the subset 83 of the plurality of struts 81. Asdepicted in FIG. 9B, the outer struts 85 are elastically deformed sincethe outer struts 85 are peripheral to the impact. The second struts 87have begun plastic deformation and buckling. The buckling of the thirdstruts 88 is more pronounced. The central struts 80 have fractured.

FIG. 10 is a deceleration vs. time chart of an impact of an impactingobject 25 into a vehicle hood including a local energy absorberaccording to the present disclosure compared with a similar impact intoa hood without the local energy absorber. In FIG. 10, the horizontalaxis 101 indicates time in ms, and the vertical axis 100 indicatesdeceleration in units of g. Without being bound to any theory, it isbelieved that examples of the energy absorber 20 disclosed herein allowthe impact energy to be absorbed while reducing the decelerationexperienced by the impacting object 25. Since the energy absorbed isdirectly related to the deceleration integrated over time (the areaunder the deceleration curve), the existing energy absorber depicted bytrace 102, which begins plastic deformation at about 5.5 ms, does notabsorb sufficient energy early enough in the impact to prevent thedeceleration from climbing to the peak at about 12 ms. It is believedthat without the energy absorber, the hood bottoms out (i.e. contactsthe underhood object 14) at about 9 ms, causing the rise in decelerationas the underhood object 14 begins to elastically deform under load ofthe impact. The underhood object 14 is relatively stiff, producing thesteep deceleration curve with respect to time. In sharp contrast, thelocal energy absorber 20 of the present disclosure depicted in trace 103absorbs energy in the elastic deformation portion of the impact, (up toabout 8 ms), which is earlier than in trace 102. At about 8 ms, bucklingand plastic deformation begins, and the local energy absorber 20 beginsto fracture. Fracturing dissipates energy from the impact. Energycontinues to be absorbed by the local energy absorber 20 becausebuckling and plastic deformation are occurring and not all of the strutsthat exceed the maximum strain energy that they can absorb during theimpact will fracture at the same time. The deceleration is lower thanthe portion of the trace 103 where the struts were elastically reactingthe impact load. As a result, the peak deceleration in trace 103associated with the local energy absorber 20 of the present disclosureis lower than the peak deceleration of the trace 102 associated with thehood without the local energy absorber 20. As disclosed herein, if thedeceleration vs. time profile is less symmetrical about the peak (trace102 is relatively symmetrical), and more skewed (trace 103 is relativelyskewed) toward earlier times during the impact, evaluating Eq. 1 gives alower result.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 3 ms to about 36 ms should be interpreted toinclude not only the explicitly recited limits of from about 3 ms toabout 36 ms, but also to include individual values, such as 5 ms, 10 ms,15 ms, etc., and sub-ranges, such as from about 10 ms to about 18 ms;from about 15 ms to about 19.5 ms, etc. Furthermore, when “about” isutilized to describe a value, this is meant to encompass minorvariations (up to +/−5 percent) from the stated value.

Further, the terms “connect/connected/connection” and/or the like arebroadly defined herein to encompass a variety of divergent connectedarrangements and assembly techniques. These arrangements and techniquesinclude, but are not limited to (1) the direct communication between onecomponent and another component with no intervening componentstherebetween; and (2) the communication of one component and anothercomponent with one or more components therebetween, provided that theone component being “connected to” the other component is somehow inoperative communication with the other component (notwithstanding thepresence of one or more additional components therebetween).

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it will beapparent to those skilled in the art that the disclosed examples may bemodified. Therefore, the foregoing description is to be considerednon-limiting.

What is claimed is:
 1. A vehicle hood covering an object, comprising: aninner surface of the vehicle hood facing the object and spaced from theobject, and an outer surface of the vehicle hood opposite the innersurface; and a local energy absorber operatively attached to the innersurface of the vehicle hood, wherein the local energy absorber is amultiply-connected structure, including: a wall defining an interiorsurface having symmetry about a central plane normal to the innersurface of the vehicle hood; and a plurality of apertures defined in thewall symmetrically about the central plane to initiate buckling andfracture in the wall during an impact applied to the outer surfacedefining an impact event having a duration of less than 20 milliseconds.2. The vehicle hood as defined in claim 1 wherein the local energyabsorber is fabricated by extruding the wall as a single extrudatethrough a die, then forming the plurality of apertures.
 3. The vehiclehood as defined in claim 2 wherein the plurality of apertures are formedby machining or laser cutting as the extrudate exits the die before thelocal energy absorber is divided from the extrudate.
 4. The vehicle hoodas defined in claim 1 wherein: a first intersection of the wall and atop plane normal to the central plane defines a first simple closedconvex curve; and a second intersection of the wall and a bottom planeparallel to the top plane defines a second simple closed convex curve.5. The vehicle hood as defined in claim 4 wherein the second simpleclosed convex curve is congruent to the first simple closed convexcurve.
 6. The vehicle hood as defined in claim 5 wherein: the firstsimple closed convex curve is a circle; and the wall defines a rightcircular cylinder.
 7. The vehicle hood as defined in claim 5 wherein:the first simple closed convex curve is an ellipse or a stadium; and thewall defines a right elliptical cylinder or a right stadium cylinder. 8.The vehicle hood as defined in claim 5 wherein the local energy absorberis fabricated by extruding the wall as a single extrudate through a die,then forming the plurality of apertures in the wall.
 9. The vehicle hoodas defined in claim 8 wherein the plurality of apertures are formed bymachining or laser cutting as the extrudate exits the die before thelocal energy absorber is divided from the extrudate.
 10. The vehiclehood as defined in claim 4, wherein the local energy absorber isfabricated from a single sheet by rolling the sheet to form a conicalfrustum then permanently joining a first edge of the single sheet to asecond edge of the single sheet to form a seam by crimping or welding.11. The vehicle hood as defined in claim 10 wherein the plurality ofapertures is formed in the single sheet prior to the rolling.
 12. Thevehicle hood as defined in claim 5, wherein the local energy absorber isfabricated from a single sheet by rolling the sheet to form a closedperimeter then joining a first edge of the single sheet to a second edgeof the single sheet to form a seam by crimping or welding.
 13. Thevehicle hood as defined in claim 12 wherein the plurality of aperturesis formed in the single sheet prior to the rolling.
 14. The vehicle hoodas defined in claim 6 wherein an annular flange is defined at the secondintersection, the annular flange having an inner diameter smaller than adiameter of an inner circle defined at the second intersection.
 15. Thevehicle hood as defined in claim 7 wherein a flange is defined at thesecond intersection, the flange having an inner edge defined parallel tothe second intersection.
 16. The vehicle hood as defined in claim 5wherein a top plate is parallel to the top plane and continuouslyconnected to the wall at the first intersection.
 17. The vehicle hood asdefined in claim 2 wherein the local energy absorber is formed from amagnesium alloy.
 18. The vehicle hood as defined in claim 8 wherein thelocal energy absorber is formed from a magnesium alloy.
 19. The vehiclehood as defined in claim 1, wherein the plurality of apertures isdefined by a plurality of struts and a subset of the plurality of strutsis to, during the impact event, deform in a sequence beginning withelastic deformation, followed by plastic deformation and buckling,followed by fracture of the subset of the plurality of struts.